One of the most interesting aspects about cannibalism is that its prevalence increases upon approaching the equator - it has occurred in all major tropical areas: the Indonesian archipelago, the Caribbean islands(IIRC, "caribbean" actually stands for anthropophagist) and of course Africa.
As the environment gets more harsh, counter-intuitively the cannibalism also decreases(even if the abundance of food is lower!). The intellectually most developed races, whites and northeastern Asians have not commonly engaged in cannibalism except for the cases in which groups of sailors or explorers have gotten cut off somewhere, besieged defendants in war, those suffering of famine because of crop failure, etc. in which eating each others has been necessary for survival. Only among tropical tribes has the cannibalism been a routine practice.
The bottom line is that harsh environment has had far greater eugenic impact than cannibalism ever had, even if the weaker individuals have presumably fallen as prey.